This invention relates to a method for recovering hidden uranium dioxide and plutonium formed in an integrated fast reactor electrorefining process during operation thereof over a period of years.
Electrorefining has been used for years in processes for recovering high purity uranium and plutonium metals from an impure feed of spent nuclear fuel. In the specific case applicable to the invention, the electrorefining is carried out at the same site as the reactor, hence the term "integrated fast reactor or IFR". The electrorefining is performed in an electrolysis cell in which the impure mixture of chopped up fuel elements from the reactor forms the anode, the electrolyte is a fused salt of the metal or metals to be recovered plus an alkali metal halide or mixtures thereof and the purified metal is recovered at the cathode. In some designs, the metal collected at the cathode collects at the bottom of the cell. In general, electrorefining processes have been disclosed in the Hansen U.S. Pat. No. 2,951,793 issued Sep. 6, 1960 and in the Miller et al. U.S. Pat. No. 4,596,647 issued Jun. 24, 1986, the disclosures of which are herein incorporated by reference.
Whether the electrorefining process uses an anode pool of cadmium metal such as disclosed in the Hansen patent or a movable anode basket device as disclosed in the Miller et al. patent or a combination thereof, uranium dioxide and plutonium dioxide form during the operation of the electrorefiner over a period of years, because small amounts of oxygen are inadvertently introduced into the electrorefiner. This results in some of the uranium and plutonium not made available for electrochemical transport and prevents accurate material balances for U and Pu from being measured. In addition, these deposits make it nearly impossible to track nuclear material within the electrorefiner since the precise amount of uranium and plutonium present as oxides cannot be experimentally measured.